Testing pings out from my site has proven to be a confusing process, I think I understand now though.
WordPress both on wordpress.com and personal server installations is configured to ping ping-o-matic automatically. You can locate the settings for which services wordpress is pinging by accessing your settings menu and then proceeding to the bottom of the writing sub-page.
If your installation has the same defaults as mine did you should see http://rpc.pingomatic.com/ listed under Update Services.
To test if you have outgoing pings working you just need to test a trackback to a post somewhere out in the WWW I used Trackback Tester a wonderful service provided for free for just this purpose.
Once you’ve verified that a trackback from your site to theirs arrives you can be fairly certain that your blog won’t be having trouble reaching pingomatic.